Water and Public Health

· To demonstrate the
link between water and health and show the profound influence of water supply
and quality on public health.

· To describe the basic
classification of water-related disease.

· To describe the concept of the
faecal-oral route of disease transmission and the classic waterborne disease
cycle.

· To describe how improvements
in water supplies will lead to improvements in health and a reduction in
morbidity and mortality rates.

Introduction

Water has a profound influence on human health. At a very basic
level, a minimum amount of water is required for consumption on a daily basis
for survival and therefore access to some form of water is essential for life.
However, water has much broader influences on health and wellbeing and issues
such as the quantity and quality of the water supplied are important in
determining the health of individuals and whole communities.

The first priority must be to provide access for the whole
population to some form of improved water supply. However, access may be
restricted by low coverage, poor continuity, insufficient quantity, poor quality
and excessive cost relative to the ability and willingness to pay. Thus, in
terms of drinking-water, all these issues must be addressed if public health is
to improve. Water quality aspects, whilst important, are not the sole
determinant of health impacts.

The quality of water does, however, have a great influence on
public health; in particular the microbiological quality of water is important
in preventing ill-health. Poor microbiological quality is likely to lead to
outbreaks of infectious water-related diseases and may causes serious epidemics
to occur.

Chemical water quality is generally of lower importance as the
impact on health tend to be chronic long-term effects and time is available to
take remedial action. Acute effects may be encountered where major pollution
event has occurred or where levels of certain chemicals are high from natural
sources, such as fluoride, or anthropogenic sources, such as nitrate.

Microbiological drinking-water quality and human
health

The microbiological quality of drinking-water has been
implicated in the spread of important infectious and parasitic diseases such as
cholera, typhoid, dysentery, hepatitis, giardiasis, guinea worm and
schistosomiasis.

Many other diseases are associated with water in other ways.
Water may act positively in the control of some through its use in hygiene, and
may act as a source or vector for others where contact with water is required
for disease transmission or where agents of disease or insect vectors require
water in which to complete their life cycle. The various relationships between
water and disease are summarized in Table 1.

Water-related disease incidence worldwide

Water-related disease places an excessive burden on the
population and health services of many countries worldwide and in particular
those in developing countries. Table 2 shows estimates of the morbidity and
mortality rates of some major water-related diseases worldwide, figures which
are likely to be conservative estimates.

Table 1: Diseases related to water and sanitation

Group

Disease

Route leaving host

Route of infection

Diseases which are often water-borne

Cholera

faeces

oral

Typhoid

faeces/urine

oral

Infectious hepatitis

faeces

oral

Giardiasis

faeces

oral

Amoebiasis

faeces

oral

Dracunculiasis

cutaneous

percutaneous

Diseases which are often associated with poor hygiene

Bacillary dysentery

faeces

oral

Enteroviral diarrhoea

faeces

oral

Paratyphoid fever

faeces

oral

Pinworm (Enterobius)

faeces

oral

Amoebaisis

faeces

oral

Scabies

cutaneous

cutaneous

Skin sepsis

cutaneous

cutaneous

Lice and typhus

bite

bite

Trachoma

cutaneous

cutaneous

Conjunctivitis

cutaneous

cutaneous

Diseases which are often related to inadequate sanitation

Ascariasis

faecal

oral

Trichuriasis

faecal

oral

Hookworm (Ancylostoma/Necator)

faecal

oral/percutaneous

Diseases with part of life cycle of parasite in water

Schistosomiasis

urine/faeces

percutaneous

Diseases with vectors passing part of their life cycle in water

Dracunculiasis

cutaneous

percutaneous

adapted from Bradley, D J, London School of
Hygiene and Tropical Medicine, various

Forty per cent of mortality in children under five years of age
is related to diarrhoeal disease and it has been estimated that in 1995 more
than 1,500,000,000 episodes of diarrhoea occurred in children under five years
of age in the developing world (excluding China) and that some 4,000,000 of
these resulted in death.

These diseases are caused by the ingestion of contaminated
faecal material transmitted by the transmitted by the faecal - oral route.
Infectious agents of all types may be transmitted by the faecal - oral route via
water, including viruses (such as infectious hepatitis, rotavirus and Norwalk
agent); bacteria (such as cholera, typhoid and dysentery); and parasites (such
as Giardia, Cryptosporidium and Entamoeba).

Faecal pollution of drinking-water may be sporadic and the
degree of faecal contamination may be low or fluctuate widely. In communities
where contamination levels are low, supplies may not carry life-threatening
risks and the population may have used the same source for generations. However,
where contamination levels are high, consumers (and especially the visitors, the
very young, the old and those suffering from immuno deficiency-related disease,
for instance through malnutrition or AIDS) may be at a significant risk of
infection.

Improving water and sanitation and improvements in
health

Results of epidemiological studies into the relationship between
the quality of water supply and sanitation versus human health vary widely and
there are severe methodological difficulties involved in undertaking such
studies. Nevertheless there is sufficient evidence to support the conclusion
that improving water supply and sanitation can have a significant impact on
human health. Table 3 summarizes the findings of an extensive review of studies
of this type.

Table 3: Percentage reduction in the diarrhoea morbidity rate
attributed to improvements in water supply or excreta disposal

Type of Intervention

Number of Studies

Percentage reductionMedian

Range

All

53

22

0-100

Water quality improvements

9

16

0-90

Improvements in availability

17

25

1-100

Improvements in availability and quality of water

8

37

0-82

Improvements in excreta disposal

10

22

0-48

Source: after Esrey, Feachem and Hughes,
1985

One of the reasons for the difficulty in undertaking studies on
the health impact of improvements in water supply quality is that the faecal -
oral route includes several and multiple routes to infection as summarized in
Figure 1 below.

Figure 1: Principal elements of
faecal - oral disease transmission

This complexity of routes also demonstrates the importance of
various aspects of hygiene as complementary actions to water quality
improvements.

Clearly, the likelihood of acquiring a waterborne infection
increases with the level of contamination by pathogenic (disease-causing)
microorganisms. However, the relationship is not necessarily a simple one and
depends very much on factors such as infectious dose and host susceptibility.

Moreover there remains some doubt as to the relative importance
of drinking-water quality and other aspects of water supply on the prevalence of
infections with a faecal-oral route of transmission. For example, some agents
with a low infectious dose may be transmitted primarily from person to person
and thus improving the quality of drinking-water may not make a dramatic impact
on their prevalence in the community. Human rotavirus and some species of
Shigella fall into this category. Bacteria which are capable of
multiplication in food may follow a food-borne transmission route more readily
than waterborne.

Conversely there are other agents for example Salmonella
typhi, Vibrio cholerae, Giardia lamblia and hepatitis A virus which are
frequently transmitted via contaminated drinking-water. Where this is the case,
improvements in water quality may result in substantial reductions in
prevalence.

In those cases where transmission is not primarily water borne,
improvements in water availability and personal hygiene may be much more
important in reducing morbidity from diarrhoea and other water-borne infections.

The relative importance of drinking-water quality to the
maintenance of public health may vary with respect to a number of geographical,
social, seasonal and microbiological factors. It is not possible to state with
any confidence which aspect of water supply is the most important at any one
time or in any one location. What is becoming increasingly clear however is that
all factors relating to the quality and availability of drinking-water
are potentially important and must be taken into consideration. In this context
it is worth emphasizing that one of the few general conclusions that may be
drawn about drinking-water quality is that if faecally-derived pathogens are not
present, then endemic or epidemic waterborne disease will not occur.

Other aspects of microbiological quality

As noted above, water borne disease is not exclusively
transmitted by the faecal-oral route, although this route of disease
transmission is of overwhelming importance globally. Some other microbiological
aspects of importance are as follows:

Opportunistic and other water-associated pathogens

Opportunistic pathogens are naturally present in the environment
and normally present no risk to human health. They are able to cause disease in
people with impaired local or general immune defences. These people include the
elderly and the very young; persons with extensive burns; persons undergoing
immuno-suppressive therapy (such as following transplant surgery) and those with
immuno deficiency-related diseases (such as AIDS). Examples of opportunistic
pathogens of this type include Pseudomonas aeruginosa, certain species of
Flavobacterium, Acinetobacter, Klebsiella, Serratia, Aeromonas and some
'slow growing' mycobacteria.

Inhalation of water containing certain infectious agents may
also cause disease. This is the case with, for example, Legionella spp
(Legionnaire's disease) and Naeglaria fowleri (an occasional cause of
primary amoebic meningoencephalitis).

Cyanobacterial Toxins

Some cyanobacteria ('blue-green algae') are capable of producing
toxins, including hepatotoxins, neurotoxins and lipopolysaccharides. Few
epidemiological studies have been undertaken and little information is available
regarding the true importance of this problem. Where blooms of cyanobacteria
occur in lakes and reservoirs used for drinking-water supply a potential risk to
health exists and therefore impounded surface waters used for drinking-water
supply should be protected from contamination with nutrients.

Nuisance organisms

A number of organisms of no public health significance are
undesirable because they produce turbidity, taste or odour or because they are
visible to consumers of drinking-water. Their presence indicates that water
treatment and supply system maintenance may be defective. These include: tastes
and odours from Actinomyces and Cyanobacteria; and infestation of
water mains by animal life feeding upon microbial films, such as the crustacean
Gammarus pulex, Nais worms and the larvae of chironomids.

Chemical contamination and health

Chemical contamination of drinking-water may also have effects
on health, although in general these tend to be chronic rather than acute,
unless a specific pollution event has occurred and are therefore generally
considered of lower priority than microbiological contamination.

Chemical pollutants which affect health include nitrate,
arsenic, mercury and fluoride. In addition, there are an ever-increasing number
of synthetic organic compounds released into the environment whose effect on
human health is poorly understood, but which it appears may be carcinogenic.

Some details are given below on the four substances noted above,
however, it must be recognized that raised concentrations of any chemical known
to have an impact on human health may lead to long-term problems. In general,
water sources used for drinking-water supply should be protected from chemical
contamination through land-use control, definition of protection zones and
application of adequate wastewater treatment.

Nitrate

Excess nitrate in drinking-water has been linked to
methaemaglobinamenia in infants, the so-called 'blue-baby' syndrome. Nitrate
leads to the oxidation of normal haemoglobin to methaemoglobin which is unable
to transport oxygen to the tissues. This may result in cyanosis (a dark blue
coloration) and in some cases, asphyxiation and death.

The Guideline Value (GV) for nitrate of 50 mg/l has been set on
the basis of the acute health risk to infants and is unusual for this reason as
most GVs are set for long-term risks. Many countries are now experiencing
problems with elevated nitrate, particularly in groundwaters caused through poor
treatment and disposal of excreta, intensification of animal husbandry and
large-scale applications of inorganic and organic fertilizers.

In some countries, notably in the Countries of Central and
Eastern Europe (CCEE) such as Moldova and Romania, levels have been recorded in
shallow groundwater at up to 1000 mg/l, whilst in India anecdotal evidence
suggest levels of up to 1500 mg/l. At these levels, more widespread chronic
effects are likely to be noted including a possible greater likelihood of
gastric cancer.

Nitrate is a conservative element in natural groundwaters and
therefore once large-scale nitrate contamination has occurred, it will take a
considerable period of time before it is naturally attenuated through
de-nitrification or diluted. In these circumstances, short term measures will
include identifying alternative sources of water, for instance deeper boreholes,
or through blending with low-nitrate waters. Removal of nitrate by ion exchange
in treatment plants is expensive as most anion exchangers are non-selective for
nitrate and therefore nitrate specific resins must be used.

Long-term solutions must involve the reduction in the release of
nitrate into the environment through, for example, control of fertilizer
application and improvements in human and animal excreta treatment and disposal.

Arsenic

A provisional GV of 0.1 mg/l has been set for arsenic on the
basis of an excess cancer risk of 6 × 10-4. In some parts of the
world, natural sources of arsenic may contaminate water supplies and lead to
poisoning of the users. The most well-documented cases of arsenic poisoning from
drinking-water have come from India, where there is arsenic contamination of
large numbers of rural water supplies. Common symptoms include inflamed eyes and
skin lesions. Arsenic contamination has also been noted in southern Thailand and
the CCEE.

Most natural arsenic comes from the reduction of arsenic
complexes caused through changing redox and pH conditions and from the oxidation
of arsenic containing minerals exposed by falling groundwater tables induced
through over abstraction or reduced recharge.

There is also increasing evidence that there is a tendency for
arsenic levels to increase in shallow groundwaters under urban areas. This has
been particularly noted where conditions become anoxic, organic rich sediments
are present and arsenate compounds associated with iron are common. This has
significant implications for water supply in these areas, particularly in
low-income areas where community-based water projects may involve the sinking of
dug and wells and shallow tube wells. Arsenic may also be discharged in effluent
from a variety of industrial processes.

Control options for arsenic contamination will vary according to
the source. Arsenic derived from industrial effluents should be controlled
through proper treatment of wastes and monitored by the pollution control
agency. The control of arsenic from natural sources must include sustainable
groundwater resource management. Many of the problems noted in India result from
over-abstraction of groundwater, primarily by the agricultural sector. Arsenic
problems noted under urban areas may be more difficult to control given the
range of factors which influence whether arsenic is released.

In all cases, short-term options will include treatment of water
in home using, use of alternative sources or a switch to an alternative source,
such as deep groundwater unaffected by arsenic contamination. Arsenic may be
removed at treatment plants through a variety of processes, although like most
treatment aimed at chemical removal, increase the costs of producing
drinking-water.

Fluoride

Fluoride in drinking-water can have toxic effects in both excess
and deficiency, although WHO only set a GV of 1.5 mg/l for excess fluoride as
susceptibility in deficiency is highly dependent on nutritional status.

Excess fluoride may lead to dental or skeletal fluorosis, the
latter being a crippling disease which affects a number of areas including the
Rift valley of East Africa and parts of India, Mexico and the former Soviet
Union. However, a lack of fluoride may cause dental caries, a weakening of the
teeth, thus in some circumstances fluoride may be added to the drinking-water
supply.

The acceptable concentration of fluoride in water is in part
related to climate, as in warmer climates the quantities of water consumed are
higher thus leading to a greater risk of fluoride related problems as overall
intake increases. Susceptibility of individuals to fluorosis may also be
determined by renal impairment.

Control options for fluoride contamination of water include
blending of fluoride-rich waters with waters of low fluoride content, selection
of low-fluoride sources and removal of fluoride by treatment at public water
supply or household level. Fluoride can be successfully removed by precipitation
by use of coagulants (commonly an alum-lime mix), adsorption on activated carbon
substrates, osmosis or ion exchange. Fluoride removal is often more effective at
a water supply level and the Nalgonda technique, developed in India, has been
proven as a low-cost techniques which can operate on a variety of water supply
options ranging from piped water supplies to handpump units.

· many infectious diseases can
be classified in more than one group, for instance most diarrhoeal disease may
be transmitted by a classic water-borne route, but are also related to
inadequate quantities of water (hygiene)